Phosphorylated TAR DNA-binding protein-43: Aggregation and antibody-based inhibition.

TAR DNA-binding protein-43 (TDP-43) pathology, including fibrillar aggregates and mutations, develops in amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD) and limbic-predominant age-related TDP-43 encephalopathy (LATE). Hyperphosphorylation and aggregation of TDP-43 contribute to pathology and are viable therapeutic targets for ALS. In vivo inhibition of TDP-43 aggregation was evaluated using anti-TDP-43 antibodies with promising outcomes. However, the exact mechanism of antibody-based inhibition targeting TDP-43 is not well understood but may lead to the identification of viable immunotherapies. Herein, the mechanism of in vitro aggregation of phosphorylated TDP-43 was explored, and the anti-TDP-43 antibodies tested for their inhibitor efficacies. Specifically, the aggregation of phosphorylated full-length TDP-43 protein (pS410) was monitored by transmission electron microscopy (TEM), turbidity absorbance, and thioflavin (ThT) spectroscopy. The protein aggregates were insoluble, ThT-positive and characterized with heterogeneous morphologies (fibers, amorphous structures). Antibodies specific to epitopes 178-393 and 256-269, within the RRM2-CTD domain, reduced the formation of ß-sheets and insoluble aggregates, at low antibody loading (antibody: protein ratio = 1 µg/mL: 45 µg/mL). Inhibition outcomes were highly dependent on the type and loading of antibodies, indicating dual functionality of such inhibitors, as aggregation inhibitors or aggregation promoters. Anti-SOD1 and anti-tau antibodies were not effective inhibitors against TDP-43 aggregation, indicating selective inhibition.

Off-label use of plastic syringes with silicone oil for intravenous infusion bags of antibodies.

The formation of particulates in post-manufacture biopharmaceuticals continues to be a major concern in medical treatment. This study was designed to evaluate the content of micro-sized particles using flow imaging of antibodies in intravenous infusion bags. Intravenous immunoglobulin (IVIG) and Avastin® were selected as model drugs and plastic syringes with and without silicone oil (SO) were used to transfer the drugs into the bags (0.9% saline or 5% dextrose). Antibodies exposed to SO had significantly increased levels of microparticles in both diluents, suggesting SO accelerates particle formation, especially at a higher antibody concentration. Even before the drop stress, their count exceeded the USP guideline. Dropping the bags in the presence of SO produced larger microparticles. Meanwhile, air bubbles were retained longer in saline suggesting more protein film formation on its air-water interface. Overall, both drugs were conformationally stable and produced less particles in dextrose than in saline.

A human antibody selective for transthyretin amyloid removes cardiac amyloid through phagocytic immune cells.

Transthyretin amyloid (ATTR) cardiomyopathy is a debilitating disease leading to heart failure and death. It is characterized by the deposition of extracellular ATTR fibrils in the myocardium. Reducing myocardial ATTR load is a therapeutic goal anticipated to translate into restored cardiac function and improved patient survival. For this purpose, we developed the selective anti-ATTR antibody NI301A, a recombinant human monoclonal immunoglobulin G1. NI301A was cloned following comprehensive analyses of memory B cell repertoires derived from healthy elderly subjects. NI301A binds selectively with high affinity to the disease-associated ATTR aggregates of either wild-type or variant ATTR related to sporadic or hereditary disease, respectively. It does not bind physiological transthyretin. NI301A removes ATTR deposits ex vivo from patient-derived myocardium by macrophages, as well as in vivo from mice grafted with patient-derived ATTR fibrils in a dose- and time-dependent fashion. The biological activity of ATTR removal involves antibody-mediated activation of phagocytic immune cells including macrophages. These data support the evaluation of safety and tolerability of NI301A in an ongoing phase 1 clinical trial in patients with ATTR cardiomyopathy.

Immune response with long-term memory triggered by amorphous aggregates of misfolded anti-EGFR VHH-7D12 is directed against the native VHH-7D12 as well as the framework of the analogous VHH-9G8.

We previously demonstrated that amorphous aggregates of misfolded VHH-7D12 antibodies (VHH-Mis), a potential anti-EGFR drug, can generate a robust serum IgG response. Here we investigate the immunogenic nature, especially the specificity of the immune response induced by VHH-Mis. To this end, we used two natively folded and 77% identical anti-EGFR VHHs (VHH-7D12 and VHH-9G8) that possess a common framework but distinct complementarity determining regions (CDRs). In 60% of mice immunized with VHH-Mis, the anti-VHH-7D12 IgG titer was stronger than the anti-VHH-9G8 titer (Group-1). In the remaining mice (40%; Group-2), the anti-VHH-7D12 and anti-VHH-9G8 titer were almost identical. We rationalized these results by hypothesizing that mice in Group-1 produced IgG mostly against the VHH-7D12's CDRs, whereas in Group-2 mice, they targeted the VHH's framework. The IgG specificity against VHH-7D12 and VHH-9G8 was essentially unchanged over 17 weeks in both groups. Further, in all mice (Group-1&2) re-immunized with native VHH-7D12, the IgG titer against VHH-7D12 increased sharply but not against VHH-9G8. On the other hand, none of the three Group-1 mice re-immunized with native VHH-9G8 showed immunogenicity against VHH-7D12 nor VHH-9G8. Whereas, in Group-2 mice (three/three) re-immunized with VHH-9G8, the IgG titers against both VHHs increased but slowly. Flow-cytometric studies showed that VHH-Mis immunized mice generated a higher number of effector and central memory T-cells. Overall, these observations indicate that amorphous aggregates made of a misfolded VHH can induce serum IgG against its natively folded self and analogous VHHs having a similar framework but distinct CDRs. Furthermore, a robust long-term immune response with memory was established against its natively folded self but with a nil-to-moderate immune response against natively folded VHH analogs.

Temperature is a key determinant of alpha- and beta-synuclein membrane interactions in neurons.

Aggregation of α-synuclein (αS) leads to the hallmark neuropathology of Parkinson's disease (PD) and related synucleinopathies. αS has been described to exist in both cytosolic and membrane-associated forms, the relative abundance of which has remained unsettled. To study αS under the most relevant conditions by a quantitative method, we cultured and matured rodent primary cortical neurons for >17 days and determined αS cytosol:membrane distribution via centrifugation-free sequential extractions based on the weak ionic detergent digitonin. We noticed that at lower temperatures (4 °C or room temperature), αS was largely membrane-associated. At 37 °C, however, αS solubility was markedly increased. In contrast, the extraction of control proteins (GAPDH, cytosolic; calnexin, membrane) was not affected by temperature. When we compared the relative distribution of the synuclein homologs αS and ß-synuclein (ßS) under various conditions that differed in temperature and digitonin concentration (200-1200 µg/ml), we consistently found αS to be more membrane-associated than ßS. Both proteins, however, exhibited temperature-dependent membrane binding. Under the most relevant conditions (37 °C and 800 µg/ml digitonin, i.e., the lowest digitonin concentration that extracted cytosolic GAPDH to near completion), cytosolic distribution was 49.8% ± 9.0% for αS and 63.6% ± 6.6% for ßS. PD-linked αS A30P was found to be largely cytosolic, confirming previous studies that had used different methods. Our work highlights the dynamic nature of cellular synuclein behavior and has important implications for protein-biochemical and cell-biological studies of αS proteostasis, such as testing the effects of genetic and pharmacological manipulations.

Differences in Cellular Clearing Mechanisms of Aggregates of Two Subtypes of HLA-B27.

Ankylosing spondylitis (AS) belongs to a group of diseases, called spondyloarthropathies (SpA), that are strongly associated with the genetic marker HLA-B27. AS is characterized by inflammation of joints and primarily affects the spine. Over 160 subtypes of HLA-B27 are known, owing to high polymorphism. Some are strongly associated with disease (e.g., B*2704), whereas others are not (e.g., B*2709). Misfolding of HLA-B27 molecules [as dimers, or as high-molecular-weight (HMW) oligomers] is one of several hypotheses proposed to explain the link between HLA-B27 and AS. Our group has previously established the existence of HMW species of HLA-B27 in AS patients. Still, very little is known about the mechanisms underlying differences in pathogenic outcomes of different HLA-B27 subtypes. We conducted a proteomics-based evaluation of the differential disease association of HLA B*2704 and B*2709, using stable transfectants of genes encoding the two proteins. A clear difference was observed in protein clearance mechanisms: whereas unfolded protein response (UPR), autophagy, and aggresomes were involved in the degradation of B*2704, the endosome-lysosome machinery was primarily involved in B*2709 degradation. These differences offer insights into the differential disease association of B*2704 and B*2709.

Glycosylation decreases aggregation and immunogenicity of adalimumab Fab secreted from Pichia pastoris.

Glycoengineering of therapeutic proteins has been applied to improve the clinical efficacy of several therapeutics. Here, we examined the effect of glycosylation on the properties of the Fab of the therapeutic antibody, adalimumab. An N-glycosylation site was introduced at position 178 of the H chain constant region of adalimumab Fab through site-directed mutagenesis (H:L178N Fab), and the H:L178N Fab was produced in Pichia pastoris. Expressed mutant Fab contained long and short glycan chains (L-glyco Fab and S-glyco Fab, respectively). Under the condition of aggregation of Fab upon pH shift-induced stress, both of L-glyco Fab and S-glyco Fab were less prone to aggregation, with L-glyco Fab suppressing aggregation more effectively than the S-glyco Fab. Moreover, the comparison of the antigenicity of glycosylated and wild-type Fabs in mice revealed that glycosylation resulted in the suppression of antigenicity. Analysis of the pharmacokinetic behaviour of the Fab, L-glyco Fab and S-glyco Fab indicated that the half-lives of glycosylated Fabs in the rats were shorter than that of wild-type Fab, with L-glyco Fab having a shorter half-life than S-glyco Fab. Thus, we demonstrated that the glycan chain influences Fab aggregation and immunogenicity, and glycosylation reduces the elimination half-life in vivo.

RNF115 plays dual roles in innate antiviral responses by catalyzing distinct ubiquitination of MAVS and MITA.

MAVS and MITA are essential adaptor proteins mediating innate antiviral immune responses against RNA and DNA viruses, respectively. Here we show that RNF115 plays dual roles in response to RNA or DNA virus infections by catalyzing distinct types of ubiquitination of MAVS and MITA at different phases of viral infection. RNF115 constitutively interacts with and induces K48-linked ubiquitination and proteasomal degradation of homeostatic MAVS in uninfected cells, whereas associates with and catalyzes K63-linked ubiquitination of MITA after HSV-1 infection. Consistently, the protein levels of MAVS are substantially increased in Rnf115-/- organs or cells without viral infection, and HSV-1-induced aggregation of MITA is impaired in Rnf115-/- cells compared to the wild-type counterparts. Consequently, the Rnf115-/- mice exhibit hypo- and hyper-sensitivity to EMCV and HSV-1 infection, respectively. These findings highlight dual regulation of cellular antiviral responses by RNF115-mediated ubiquitination of MAVS and MITA and contribute to our understanding of innate immune signaling.

Perfusion reduces bispecific antibody aggregation via mitigating mitochondrial dysfunction-induced glutathione oxidation and ER stress in CHO cells.

One major challenge observed for the expression of therapeutic bispecific antibodies (BisAbs) is high product aggregates. Aggregates increase the risk of immune responses in patients and therefore must be removed at the expense of purification yields. BisAbs contain engineered disulfide bonds, which have been demonstrated to form product aggregates, if mispaired. However, the underlying intracellular mechanisms leading to product aggregate formation remain unknown. We demonstrate that impaired glutathione regulation underlies BisAb aggregation formation in a CHO cell process. Aggregate formation was evaluated for the same clonal CHO cell line producing a BisAb using fed-batch and perfusion processes. The perfusion process produced significantly lower BisAb aggregates compared to the fed-batch process. Perfusion bioreactors attenuated mitochondrial dysfunction and ER stress resulting in a favorable intracellular redox environment as indicated by improved reduced to oxidized glutathione ratio. Conversely, mitochondrial dysfunction-induced glutathione oxidation and ER stress disrupted the intracellular redox homeostasis, leading to product aggregation in the fed-batch process. Combined, our results demonstrate that mitochondrial dysfunction and ER stress impaired glutathione regulation leading to higher product aggregates in the fed-batch process. This is the first study to utilize perfusion bioreactors as a tool to demonstrate the intracellular mechanisms underlying product aggregation formation.

Polyglutamine-Related Aggregates Can Serve as a Potent Antigen Source for Cross-Presentation by Dendritic Cells.

Protective MHC class I-dependent immune responses require an overlap between repertoires of proteins directly presented on target cells and cross-presented by professional APC, specifically dendritic cells. How stable proteins that rely on defective ribosomal proteins for direct presentation are captured for cell-to-cell transfer remains enigmatic. In this study, we address this issue using a combination of in vitro (C57BL/6-derived mouse cell lines) and in vivo (C57BL/6 mouse strains) approaches involving stable and unstable versions of OVA model Ags displaying defective ribosomal protein-dependent and -independent Ag presentation, respectively. Apoptosis, but not necrosis, of donor cells was found associated with robust global protein aggregate formation and captured stable proteins permissive for cross-presentation. Potency of aggregates to serve as Ag source was directly demonstrated using polyglutamine-equipped model substrates. Collectively, our data implicate global protein aggregation in apoptotic cells as a mechanism that ensures the overlap between MHC class I epitopes presented directly or cross-presented by APC and demonstrate the unusual ability of dendritic cells to process stable protein aggregates.

Assessment of the role of afucosylated glycoforms on the in vitro antibody-dependent phagocytosis activity of an antibody to Aß aggregates.

The terminal sugars of Fc glycans can influence the Fc-dependent biological activities of monoclonal antibody therapeutics. Afucosylated N-glycans have been shown to significantly alter binding to FcγRIIIa and affect antibody-dependent cell-mediated cytotoxicity (ADCC). Therefore, in order to maintain and ensure safety and efficacy for antibodies whose predominant mechanism of action (MOA) is ADCC, afucosylation is routinely monitored and controlled within appropriate limits. However, it is unclear how the composition and levels of afucosylated N-glycans can modulate the biological activities for a recombinant antibody whose target is not a cell surface receptor, as is the case with ADCC. The impact of different types and varying levels of enriched afucosylated N-glycan species on the in vitro bioactivities is assessed for an antibody whose target is aggregated amyloid beta (Aß). While either the presence of complex biantennary or high mannose afucosylated glycoforms significantly increased FcγRIIIa binding activity compared to fucosylated glycoforms, they did not similarly increase aggregated Aß uptake activity mediated by different effector cells. These experiments suggest that afucosylated N-glycans are not critical for the in vitro phagocytic activity of a recombinant antibody whose target is aggregated Aß and uses Fc effector function as part of its MOA.

Intrahepatic heteropolymerization of M and Z alpha-1-antitrypsin.

The α-1-antitrypsin (or alpha-1-antitrypsin, A1AT) Z variant is the primary cause of severe A1AT deficiency and forms polymeric chains that aggregate in the endoplasmic reticulum of hepatocytes. Around 2%-5% of Europeans are heterozygous for the Z and WT M allele, and there is evidence of increased risk of liver disease when compared with MM A1AT individuals. We have shown that Z and M A1AT can copolymerize in cell models, but there has been no direct observation of heteropolymer formation in vivo. To this end, we developed a monoclonal antibody (mAb2H2) that specifically binds to M in preference to Z A1AT, localized its epitope using crystallography to a region perturbed by the Z (Glu342Lys) substitution, and used Fab fragments to label polymers isolated from an MZ heterozygote liver explant. Glu342 is critical to the affinity of mAb2H2, since it also recognized the mild S-deficiency variant (Glu264Val) present in circulating polymers from SZ heterozygotes. Negative-stain electron microscopy of the Fab2H2-labeled liver polymers revealed that M comprises around 6% of the polymer subunits in the MZ liver sample. These data demonstrate that Z A1AT can form heteropolymers with polymerization-inert variants in vivo with implications for liver disease in heterozygous individuals.

Protein aggregation and immunogenicity of biotherapeutics.

Recombinant proteins are the mainstay of biopharmaceuticals. A key challenge in the manufacturing and formulation of protein biologic products is the tendency for the active pharmaceutical ingredients to aggregate, resulting in irreversible drug loss, and an increase in immunogenicity risk. While the molecular mechanisms of protein aggregation have been discussed extensively in the literature, knowledge gaps remain in connecting the phenomenon in the context of immunogenicity of biotherapeutics. In this review, we discussed factors that drive aggregation of pharmaceutical recombinant proteins, and highlighted methods of prediction and mitigation that can be deployed through the development stages, from formulation to bioproduction. The purpose is to stimulate new dialogs that would bridge the interface between physical characterizations of protein aggregates in biotherapeutics and the functional attributes of the immune system.

Immunogenicity of Bioproducts: Cellular Models to Evaluate the Impact of Therapeutic Antibody Aggregates.

Patients treated with bioproducts (BPs) frequently develop anti-drug antibodies (ADAs) with potential neutralizing capacities leading to loss of clinical response or potential hypersensitivity reactions. Many factors can influence BP immunogenicity and could be related to the patient, the treatment, as well as to the product itself. Among these latter factors, it is now well accepted that BP aggregation is associated with an increased potential for immunogenicity, as aggregates seem to be correlated with ADA development. Moreover, the presence of high-affinity ADAs suggests a CD4 T-cell dependent adaptive immune response and therefore a pivotal role for antigen-presenting cells (APCs), such as dendritic cells (DCs). In this review, we address the in vitro methods developed to evaluate how monoclonal antibodies could trigger the immunization process by focusing on the role of aggregated antibodies in the establishment of this response. In particular, we will present the different cell-based assays that have been used to assess the potential of antibodies and their aggregates to modulate cellular mechanisms leading to activation and the biological parameters (cellular activation markers, proliferation and secreted molecules) that can be measured to evaluate the different cell activation stages and their consequences in the propagation of the immune response. Indeed, the use of such strategies could help evaluate the risk of BP immunogenicity and their role in mitigating this risk.

The immunogenicity of an anti-EGFR single domain antibody (VHH) is enhanced by misfolded amorphous aggregation but not by heat-induced aggregation.

Amorphous aggregates of therapeutic proteins can provoke an unwanted immune response (anti-drug antibodies; ADAs), but counter-examples have led to some controversy. Amorphous aggregates can possess unique biophysical and biochemical attributes depending on both the way they are generated and the protein's biophysical/biochemical properties. Here, we examine the immunogenicity of an anti-EGFR single domain antibody (VHH) in four types of amorphous aggregates: two heat-aggregated VHH incubated at 65 °C (VHH-65) and 95 °C (VHH-95), a misfolded VHH isolated from the insoluble fraction of the E. coli lysate (VHH-Ins), and a low solubility misfolded VHH produced by miss-shuffling the SS bonds of the native VHH (VHH-Mis). Biophysical and biochemical measurements indicated that VHH was indeed natively folded, monomeric, and ß-sheeted; that VHH-65 was partially unfolded and formed aggregates with a Z-average (Zave) of 771 nm; whereas VHH-95 was unfolded and formed aggregates of 1722 nm; and that both VHH-Ins and VHH-Mis were misfolded with non-native intermolecular SS bonds and formed aggregates with a Zave of 1846 nm and 1951 nm, respectively. The IgG level generated in Jcl:ICR mice determined by ELISA showed that the native VHH was barely immunogenic, VHH-95 was not immunogenic, while VHH-65 was mildly immunogenic. By contrast, the misfolded aggregates, VHH-Ins and VHH-Mis, having a Zave and an aggregation propensity similar to that of VHH-95, were highly immunogenic. These findings indicate the critical role of the biochemical and biophysical attributes of the amorphous aggregates in generating an immune response against a protein, rather than just their sizes.

Nanometer-Sized Aggregates Generated Using Short Solubility Controlling Peptide Tags Do Increase the In Vivo Immunogenicity of a Nonimmunogenic Protein.

Subvisible aggregates of proteins are suspected to cause adverse immune response, and a recent FDA guideline has recommended the monitoring of micrometer-sized aggregates (2-10 µm) though recognizing that the underlying mechanism behind aggregation and immunogenicity remains unclear. Here, we report a correlation between the immunogenicity and the size of nanometer-scaled aggregates of a small 6.5 kDa model protein, bovine pancreatic trypsin inhibitor (BPTI) variant. BPTI-19A, a monomeric and nonimmunogenic protein, was oligomerized into subvisible aggregates with hydrodynamic radii (Rh) of 3-4 nm by attaching hydrophobic solubility controlling peptide (SCP) tags to its C-terminus. The results showed that the association of nonimmunogenic BPTI into nanometer-sized subvisible aggregates made it highly immunogenic, as assessed by the IgG antibody titers of the mice's sera. Overall, the study emphasizes that subvisible aggregates, as small as a few nanometers, which are presently ignored, are worth monitoring for deciphering the origin of undesired immunogenicity of therapeutic proteins.

Herpesviruses induce aggregation and selective autophagy of host signalling proteins NEMO and RIPK1 as an immune-evasion mechanism.

Viruses manipulate cellular signalling by inducing the degradation of crucial signal transducers, usually via the ubiquitin-proteasome pathway. Here, we show that the murine cytomegalovirus (Murid herpesvirus 1) M45 protein induces the degradation of two cellular signalling proteins, the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) essential modulator (NEMO) and the receptor-interacting protein kinase 1 (RIPK1), via a different mechanism: it induces their sequestration as insoluble protein aggregates and subsequently facilitates their degradation by autophagy. Aggregation of target proteins requires a distinct sequence motif in M45, which we termed 'induced protein aggregation motif'. In a second step, M45 recruits the retromer component vacuolar protein sorting 26B (VPS26B) and the microtubule-associated protein light chain 3 (LC3)-interacting adaptor protein TBC1D5 to facilitate degradation of aggregates by selective autophagy. The induced protein aggregation motif is conserved in M45-homologous proteins of several human herpesviruses, including herpes simplex virus, Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, but is only partially conserved in the human cytomegalovirus UL45 protein. We further show that the HSV-1 ICP6 protein induces RIPK1 aggregation and degradation in a similar fashion to M45. These data suggest that induced protein aggregation combined with selective autophagy of aggregates (aggrephagy) represents a conserved viral immune-evasion mechanism.

Antiviral Immune Response as a Trigger of FUS Proteinopathy in Amyotrophic Lateral Sclerosis.

Mutations in the FUS gene cause familial amyotrophic lateral sclerosis (ALS-FUS). In ALS-FUS, FUS-positive inclusions are detected in the cytoplasm of neurons and glia, a condition known as FUS proteinopathy. Mutant FUS incorporates into stress granules (SGs) and can spontaneously form cytoplasmic RNA granules in cultured cells. However, it is unclear what can trigger the persistence of mutant FUS assemblies and lead to inclusion formation. Using CRISPR/Cas9 cell lines and patient fibroblasts, we find that the viral mimic dsRNA poly(I:C) or a SG-inducing virus causes the sustained presence of mutant FUS assemblies. These assemblies sequester the autophagy receptor optineurin and nucleocytoplasmic transport factors. Furthermore, an integral component of the antiviral immune response, type I interferon, promotes FUS protein accumulation by increasing FUS mRNA stability. Finally, mutant FUS-expressing cells are hypersensitive to dsRNA toxicity. Our data suggest that the antiviral immune response is a plausible second hit for FUS proteinopathy.

The viral protein corona directs viral pathogenesis and amyloid aggregation.

Artificial nanoparticles accumulate a protein corona layer in biological fluids, which significantly influences their bioactivity. As nanosized obligate intracellular parasites, viruses share many biophysical properties with artificial nanoparticles in extracellular environments and here we show that respiratory syncytial virus (RSV) and herpes simplex virus type 1 (HSV-1) accumulate a rich and distinctive protein corona in different biological fluids. Moreover, we show that corona pre-coating differentially affects viral infectivity and immune cell activation. In addition, we demonstrate that viruses bind amyloidogenic peptides in their corona and catalyze amyloid formation via surface-assisted heterogeneous nucleation. Importantly, we show that HSV-1 catalyzes the aggregation of the amyloid ß-peptide (Aß42), a major constituent of amyloid plaques in Alzheimer's disease, in vitro and in animal models. Our results highlight the viral protein corona as an acquired structural layer that is critical for viral-host interactions and illustrate a mechanistic convergence between viral and amyloid pathologies.

The Otubain YOD1 Suppresses Aggregation and Activation of the Signaling Adaptor MAVS through Lys63-Linked Deubiquitination.

MAVS is a critical adaptor required for activating an innate antiviral immune response against viral infection. The activation of MAVS requires modification of the Lys63-linked ubiquitination and formation of prion-like aggregates. However, the molecular mechanisms regulating MAVS activity remain largely obscured. In this study, we identified a deubiquitinase YOD1, also known as a member of the ovarian tumor family, as a negative regulator of MAVS activation in both human and murine cells. YOD1 was recruited to mitochondria to interact with MAVS through its UBX and Znf domains after viral infection. Subsequently, YOD1 cleaved the K63-linked ubiquitination and abrogated the formation of prion-like aggregates of MAVS, which led to attenuation of IRF3, P65 activation, and IFN-ß production. Knockdown of YOD1 potentiated IRF3 and P65 activation, IFN-ß production, and antiviral innate immune response to RNA virus. Our findings thus provided, to our knowledge, novel insights into the regulatory cascade of the cellular antiviral response through YOD1-mediated K63-linked deubiquitination and aggregation of MAVS.